Cointegrative vectors were the first type of vector developed for transferring foreign DNA from the bacterium Agrobacterium to plant cells, for use in plant genetic engineering (1). Although cointegrative vectors may be relatively difficult to work with in practice, compared with the alternative binary vectors, they offer plasmid stability in the bacterial cell.
The general concept of using cointegrative vectors relies on homologous recombination within Agrobacterium to introduce into a modified T-DNA the DNA to be transferred to the plant cell. First, the DNA to be transferred is introduced into an intermediate cloning vector based on an Escherichia coli plasmid. The intermediate vector that contains the foreign DNA is introduced by conjugation into Agrobacterium that contains the cointegrative vector. The cointegrative vector is a Ti plasmid from which the T-DNA genes that encode oncogenic function have been removed and/or replaced with a sequence that is also contained in the intermediate vector. The intermediate vector is not stable in Agrobacterium. Homologous recombination between the intermediate vector and the cointegrative vector results in transferring the foreign DNA to the cointegrative vector. These vectors are designed so that once the foreign DNA, is integrated into the cointegrative vector, it is located between its border sequences. The most generally used cointegrative vector system is the "split-end vector system" (2)
